Motor control center unit with retractable stab assembly and methods for using the same

ABSTRACT

A motor control unit (MCU) and methods of operating the same are provided. The MCU includes a housing enclosing a retractable stab assembly (RSA) having stabs attached thereto. The MCU further includes a bracket assembly having a mount for securing the bracket assembly to the RSA, guiderails for slideably engaging the RSA to facilitate the extending and retracting motion, and a lead screw accessible via an opening in the front of the housing. Rotating the lead screw causes the RSA to extend and retract which engages and disengages the stabs. The MCU also includes a motor assembly having a drive motor coupled to a drive shaft. The motor rotates the shaft in response to control signals from a remote-device. The motor assembly attaches to the housing such that the rotation of the shaft in response to the signals rotates the lead screw to engage and disengage the stabs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International ApplicationNo.: PCT/US2016/017430 filed Feb. 11, 2016, and claims the benefitthereof, the entire content of which is hereby incorporated herein byreference. The International Application claims priority and the benefitof International Application No.: PCT/US2015/19142 filed on Mar. 6,2015, the disclosure of which is hereby incorporated by referenceherein.

TECHNICAL FIELD

Aspects of the present invention relate generally to motor controlcenters (MCC), and more particularly, to MCC subunits and related stabassemblies, and methods of using the same.

BACKGROUND

A motor control center is a multi-compartment enclosure comprising apower bus system to distribute electrical power, on a common bus system,to one or more motor control units within the motor control centersections. The motor control units are typically constructed to beremovable units that have individual sealed doors on the motor controlcenter section. These motor control units may contain various motorcontrol and motor protection components, such as motor controllers,starters, contactor assemblies, overload relays, circuit breakers, motorcircuit protectors, various disconnects, and similar devices forelectric motors. The motor control units connect to the supply powerlines of the motor control center and supply power to the line side ofthe motor control devices, for operation of motors. Motor controlcenters are oftentimes used in factories and industrial facilities whichutilize high power electrical motors, pumps, and other loads.

Typically, when installing or removing motor control units, the powersupply lines are connected. To remove the motor control units, a door ofthe motor control unit or motor control center section is opened and anoperator manually pulls the motor control unit to separate theconductive contacts or stabs from the bus system, thereby disconnectingthe power supply. Installation of a motor control units are accomplishedin a similar manner, whereby the operator manually pushes the bucketinto a compartment of the motor control center section to engage thestabs with the bus system, thus connecting the system to supply power.In some instances, the stabs may be difficult to maneuver manually (pushand pull) when an operator is supporting the entire bucket or when thestabs are not visible. These difficulties may lead to numerous hazards(e.g., shocks/misfires, an arc or arc flash) that may be harmful anddangerous to the operators. It would therefore be desirable to design amotor control unit that overcomes the aforementioned difficulties.

SUMMARY

In an exemplary embodiment, a system for operating a control unit in amotor control center is provided. The system includes a motorizedcontrol unit operatively connected to a pendant, and configured toreceiving one or more control signals from the pendant. The motorizedcontrol unit includes at least a housing adapted to at least partiallyenclose one or more electrical components therein. The motorized controlunit further includes a retractable stab assembly enclosed within thehousing. The retractable stab assembly includes a stab housing havingone or more stabs extending rearwardly therefrom for engaging a powerbus in the motor control center. The stab housing is adapted toslideably engage one or more guide rails within the motorized controlunit for extending and retracting the retractable stab assembly, e.g.,along an axis of the guiderails. The motorized control unit may furtherinclude a lead screw assembly operatively connected to the stab housing.The lead screw assembly includes at least a lead screw rotatable toextend and retract the retractable stab assembly along the guiderails.The motorized control unit further includes a motor assembly selectivelyattached to a front of the motorized control unit housing and isoperatively connected to the retractable stab assembly for extending andretracting the retractable stab assembly in response to the controlsignals. The motor assembly includes a drive motor operatively coupledto a drive shaft. The drive shaft extends in a rearward direction fromthe motor assembly to engage the lead screw within the housing. Thedrive motor is operable to rotate the lead screw, via the drive shaft,in response to the control signals from the pendant, which correspondsto commands initiated at the pendant, via one or more controls of thependant, by an operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective exploded view of a motor control centerhaving a motor control unit with retractable stab assembly, inaccordance with the disclosure provided herein;

FIG. 2 illustrates a perspective view of the motor control unit withretractable stab assembly, in accordance with the disclosure providedherein;

FIG. 3A illustrates a schematic, perspective view of an upper panelassembly of the motor control unit, in accordance with the disclosureprovided herein;

FIG. 3B illustrates another schematic, perspective view of the upperpanel assembly of FIG. 3A with an inaccessible lead screw assembly viathe upper panel assembly, in accordance with the disclosure providedherein;

FIG. 3C illustrates a further schematic, perspective view of the upperpanel assembly of FIG. 3A with an accessible lead screw assembly, inaccordance with the disclosure provided herein;

FIG. 3D illustrates yet a further schematic perspective view of theupper panel assembly of FIG. 3B with a disengaged stab assembly inaccordance with the disclosure provided herein;

FIG. 4 illustrates a perspective view of the motor control unit backpanel, in accordance with the disclosure provided herein;

FIG. 5A illustrates a schematic, perspective view, of a lead screwassembly in an engaged position, in accordance with the disclosureprovided herein;

FIG. 5B illustrates a schematic, perspective view of the lead screwassembly of FIG. 5A in a disengaged position, in accordance with thedisclosure provided herein;

FIG. 6A illustrates a schematic, perspective view of a retractable stabassembly, in accordance with the disclosure provided herein;

FIG. 6B illustrates another schematic, perspective view of the stabassembly of FIG. 6A;

FIG. 6C illustrates a further schematic, perspective view of the stabassembly of FIG. 6A;

FIG. 7A illustrates a perspective view of a shutter assembly in a closedposition, in accordance with the disclosure provided herein;

FIG. 7B illustrates a perspective view of the shutter assembly of FIG.7A in an open position, in accordance with the disclosure providedherein;

FIG. 8 illustrates a flow chart for a process of disengaging stabs of amotor control unit, in accordance with the disclosure provided herein;

FIG. 9 illustrates an exemplary embodiment of a remote-controlled systemfor operating an embodiment of the motor control unit, in accordancewith the disclosure provided herein;

FIG. 10 illustrates a perspective view of a motorized control unit, inaccordance with the disclosure provided herein;

FIG. 11 illustrates a side perspective view of an embodiment of a motorassembly operatively attached to a motor control unit, in accordancewith the disclosure provided herein;

FIG. 12 illustrates a side cross-sectional view of an embodiment of themotorized control unit, in accordance with the disclosure providedherein;

FIG. 13 illustrates a side cross-sectional view of a motor assembly,e.g., of the motorized control unit, in accordance with the disclosureprovided herein;

FIG. 14 illustrates a rear perspective view of an embodiment of themotor assembly, in accordance with the disclosure provided herein; and

FIG. 15 illustrates a flow chart for a process of disengaging stabs ofan exemplary embodiment of the motorized control unit, in accordancewith the disclosure provided herein.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating embodiments of the subject matter herein only and not forlimiting the same, FIG. 1 illustrates a side perspective view of a motorcontrol center (MCC) 100. The MCC 100 includes one or more MCC sections110 configured to house one or more motor control units (MCU) 200. TheMCC section 110 may be generally rectangular in shape, and includes aplurality of panels arranged to compartmentalize the MCC section 110.For example, each MCC section 110 may include a pair of opposed sidepanels 112, a top 114 and bottom panel 116, a back panel 118, and one ormore intermediate panels 120 arranged such that the panels collectivelydefine one or more openings or compartments 124 adapted for at leastpartially receiving the MCU 200 therein.

In a further embodiment, the MCC section 110 may include a door panel122 for encapsulating the MCU 200 within the defined opening of the MCCsection 110. The door panel 122 may be one of the panels of the MCU 200.In an embodiment where multiple MCC sections 110 are provided, one ormore of the above panels may be common between or across the multipleMCC sections 110. The panels may be constructed from a single piece ofmaterial having a common surface (e.g., sheet metal), or a plurality ofsheets, frames and interlocking assemblies adapted to selectively mounttogether for providing a panel-like structure. The frames andinterlocking assemblies may be selectively mounted by a fastening means.In an exemplary embodiment, the fastening means may be, for example, oneor more screws, nuts and bolts, and rivets applied via mechanicalfastening process through one or more apertures and/or connecting pointsof the sheets, frames, and interlocking assemblies. Alternatively, thefastening means may be applied via a more permanent-like mountingprocess, e.g., welding. A combination of both processes may also be usedto achieve the desired arrangement for panels of the MCC section 110, orfor arranging and/or assembling the panels and assemblies describedherein. The MCC section 110 may further include one or more power buses702 (see FIG. 7A) vertically or horizontally arranged at the rear of theMCC section 110, at or proximate to the back panel 118. In a furtherembodiment, where the one or more power buses 702 is arranged in theback panel 118, the back panel 118 may be a separate power bus housing700 (see FIG. 7A) as described herein, which may be operably connectedto the MCC section 110. The power bus 702 is adapted to interface withone or more components of the MCU 200 for providing power to the same.

With continued reference to FIG. 1, and now FIG. 2, a perspective viewof an embodiment of the MCU 200 with retractable stab assembly 500 isprovided. The MCU 200 comprises a housing 202 shaped for being at leastpartially received within the compartment 124 of the MCC section 110.The housing 202 may be made up of one or more panels and/or assembliesconfigured for removably securing the MCU 200 within the MCC section110, and to partially or fully enclose one or more components therein.In the embodiment of FIG. 2, the MCU 200 can include a front panel 210,a back panel 220, a lower panel 230, and an upper panel 240. Similar tothe panels of the MCC section 110, the panels of the MCU 200 may be madefrom a single piece of material or plurality of frames and/orinterlocking assemblies selectively mounted to one another by thefastening means discussed herein, or by any means known to persons ofordinary skill in the art. When assembled, the panels of the housing 202may define a shape (e.g., generally rectangular) adapted to be removablysecured within the MCC section 110, and to have one or more electricalcomponents and/or assemblies mounted therein. Examples of electricalcomponents may include, among other assemblies that will be discussedbelow, a contactor or a solid-state motor controller, overload relays toprotect the motor, fuses or a circuit breaker to isolate a motorcircuit, or combinations thereof.

With continue reference to the figures, the front panel 210 may includeone or more openings arranged in a non-uniform or uniform manner, andfor at least partially receiving therebetween one or more assemblies.FIG. 2 illustrates a switch assembly opening (not shown) having a switchassembly 300 at least partially installed therebetween, and a motorassembly opening (not shown) for receiving, e.g., an embodiment of apanel assembly 350 partially installed therebetween. Additional openingsmay also be provided for at least partially receiving a fastening meanstherebetween for selectively mounting the front panel 210 to one or moreof the other panels of the MCU 200. In one embodiment, the openings maybe one or more fastening apertures 216 or recesses extending at leastpartially through the front panel 210 for receiving the fastening means,and arranged to correspond with fastening apertures and/or recesses ofthe other panels. The fastening apertures 216 may include a threadedportion that corresponds to a threaded portion of the fastening means(e.g., threaded screw).

In a further embodiment, the front panel 210 may include a lead screwaccess opening 218 for providing access to a lead screw assembly 600,for example, when the front panel 210 is in a closed position. In anexemplary embodiment, the lead screw access opening 218 may be its ownopening in the front panel 210, or in a further embodiment, an openingin a drive panel 352 of the panel assembly 350. In yet a furtherembodiment, the front panel 210 may include an indicator opening 232 forviewing one or more status indications for the MCU 200, e.g., engaged ordisengaged stabs status, live unit status, lock status etc. Similar tothe lead screw access opening 218, the indicator opening 232 may be itsown opening on the front panel 210, or an opening on one or moreassemblies, e.g., switch assembly 300. The front panel 210 may furtherinclude one or more hinge assemblies 222 for mounting one side of thefront panel 210 to one of the side panels (not shown) of the MCU 200, astructure of the MCC section 110, or in certain configurations, both.

As previously disclosed, the drive panel 352 may include one or moreopenings for providing access to the lead screw 610. The drive panel 352may further include additional openings, for example, fasteningapertures for fastening the drive panel 352 to the front panel 210 orother panels of the MCU 200. The panel assembly 350 may further includeone or more panel covers 354 for covering the openings of the drivepanel 352. For example, FIG. 2 shows one panel cover 354 for coveringthe lead screw access opening 218. The panel cover 354 may include oneor more openings 356 for at least partially receiving a fastening meanstherebetween, and for slideably mounting the panel cover 354 to thedrive panel 352 or front panel 210.

With continued reference to the figures, the switch assembly 300 mayinclude a switch panel 302 having a switch opening 304 for at leastpartially receiving a switch 310 therebetween. The switch panel 302 mayinclude additional openings similar to the openings of the drive panel352, e.g., fastening apertures for fastening the switch panel to thefront panel 210, indicator openings 232 or lead screw access openings218. The switch 310 may be operably connected to a switch control board,circuit breaker, or the like, having one or more components for poweringon/off one or more electrical components of the MCU 200. For example, asdescribed herein, in one embodiment, the switch 310 may control theoperability any motor attached to the MCU 200 by controlling limitingmotors ability to rotate the lead screw 610 to extend or retract thestab assembly 500.

In a further embodiment, the switch 310 may be operably connected to oneor more components, frames or interlocks in an upper panel assembly 400(FIG. 3). In this embodiment, the switch assembly 300 may include one ormore frames or interlocks (not shown) selectively attached or fastenedby a fastening means to one or more frames or interlocks of the upperpanel assembly 400 for shifting the upper panel assembly 400 from afirst position to a second position. For example, when the switch 300 isin the live position, access to the lead screw 610 is restricted withthe upper panel assembly 400 in the first position (FIG. 3B), whereasaccess to the lead screw 610 is provided with the switch in the off/deadposition and the upper panel assembly 400 in the second position (FIG.3C).

Referring now to FIGS. 3A-3D, an embodiment of the upper panel 240 isprovided of the MCU 200 is provided. The upper panel 240 may be formedfrom a single-piece of material in one embodiment, e.g., sheet metal, orin another embodiment, or a combination of both. In an embodiment wherethe upper panel 240 is formed from one or more frames and interlockingassemblies coupled together, the one or more frames and interlockingassemblies coupled together make up the upper panel assembly 400. Theupper panel assembly 400 may be configured such that at least a portionthereof is operably moveable from a first position to a second position,e.g., upwards or downwards. In the embodiment of FIG. 3A, the upperpanel assembly 400 includes a first support bracket 402 comprising afirst portion 404, a second intermediate portion 406, and a thirdportion 408. The first portion 404 and third portion 408 are connectedvia the second intermediate portion 406, and at least partially extendsin a first direction, e.g., downwardly, beyond the second intermediateportion 406.

In one embodiment, the first 404, second 406, and third portion 408 maybe individual frames or interlocks connected via, for example, afastening means as described herein, or in another embodiment, theportions may be integral formed. In a further embodiment, the portionsmay be formed from a single piece of material have one or more bends(i.e., bent portions) defining the first 404, second 406, and thirdportions 408. The first portion 404, second portion 406, and thirdportion 408 can further include one or more fastening apertures adaptedto receive a fastening means therebetween for operably coupling theupper panel assembly 400 to one or more other frames or assemblies ofthe MCU 200, for example, the switch assembly 300.

The first portion 404 may further include a first extension 410. Thefirst extension 410 may be positioned substantially perpendicular to thefirst portion 404, such that it extends in a rearward direction from thefirst portion 404 towards the back panel 220. The first extension 410may be formed from the same piece of material as the first portion 404,or coupled to the first portion 404 by a fastening means. As illustratedin FIG. 3A, the first extension 410 can be formed from the same piece ofmaterial, and is bent in a substantially rearward direction from thefirst portion 404. The first extension 410 may further include a firstrestrictor piece 412. The first restrictor piece 412 may extendsubstantially perpendicularly to the first extension 410 in an upwarddirection e.g., protruding upwardly. As shown exemplarily in FIG. 3A,the first restrictor piece 412 extends from one side of the firstextension 410. The first restrictor piece 412 may be formed from thesame piece of material as the first extension 410, or be coupled to thefirst extension 410 by a fastening means, or any other means known topersons having ordinary skill in the art. In an embodiment where thefirst extension 410 and the first restrictor piece 412 are formed fromthe same piece of material, the first restrictor piece 412 may be bentto the desired substantially perpendicular position. In operation, forexample, when the MCU 200 is live (i.e., the stabs 520 are engaged), thefirst restrictor piece 412 may be operably adapted to limit or restrictmovement of the MCU 200 from the MCC section 110.

The third portion 408 may include a means for accessing a lead screw610. As shown in FIG. 3A, the means for accessing the lead screw can bean access bracket 414 having one or more access bracket openings 416adapted or sized to provide access to the lead screw 610, or in afurther non-limiting embodiment, for receiving e a lead screw tool (notshown) for adjusting the lead screw 610 at least partially therebetween.The access bracket 414 may be made from one or more frames selectivelyattached to form the access bracket 414, as shown in FIG. 3A, or theaccess bracket 414 may be made from a single piece of material, similarto the material of the third portion 408. The access bracket 414 may beselectively attached to the third portion 408 by the fastening meansdisclosed herein or by any means known to person of ordinary skill inthe art. Additionally, the access bracket 414 may be integrally formedwith at least a portion of the third portion 408. As used herein,integrally formed means to couple such that the pieces are relativelypermanently joined. In one embodiment, the access bracket 414 may extendin a generally downward direction, opposite from the direction of thefirst restrictor piece 412. Additionally, the access bracket 414 may bebent such that at least a portion of the access bracket 414, i.e., afirst bent portion 418, extends in a substantially rearward directiontowards the back panel 220. The access bracket 414 may be bent further,i.e., includes a second bend, such that at least a portion of the accessbracket 414 i.e., the second bent portion 420, extends in asubstantially upward, similar to the direction of the first restrictorpiece 412. This second bent portion 420 of the access bracket may beoperable to restrict movement of the stab assembly 500 in instanceswhere the stabs 520 may be partially engaged.

In operation, at least a portion of the upper panel assembly 400 (e.g.,access bracket 414) can shift in a relatively upwards or downwardsdirection for aligning the access bracket opening 416 with the leadscrew access opening 218. Shifting of the access bracket 414 maycorrespond to the live/dead status of the MCU 200, i.e., turning on oroff the switch 310. For example, when an installed MCU 200 is in thelive status, i.e., the switch 310 is on, the upper panel assembly 400may in a first position to restrict movement of the MCU 200 and limitaccess to the lead screw assembly 600. When an operator switches off theswitch 310, at least a portion of the upper panel assembly 400 may shiftfrom a first position (FIG. 3B) to a second position (FIG. 3C), therebyproviding access to the lead screw assembly 600, and allowing for theMCU 200 to be removed once the stabs 520 are disengaged.

Referring to FIG. 4, a perspective view of an embodiment of the backpanel 220 of the MCU 200 is illustrated. The back panel 220 may beconstructed from a material similar to that of the other panels of theMCU 200, and may include a plurality of openings, e.g., apertures, forreceiving a means for selectively attaching (e.g., the fastening means)the back panel 220 to one or more of the other panels of the MCU 200. Inthe embodiment of FIG. 3, the back panel 220 includes an upper portion222 and a lower portion 224. The upper portion 222 and lower portion 224may be formed from a single piece of material, or be formed frommultiple pieces of materials connected to one another by, for example,the fastening means disclosed herein. In either configuration of theback panel 220, single or multi-piece construction, the upper portion222 may include an opening 226 adapted for at least partially having thestab assembly 500 extending outward therefrom. In one embodiment, thestab assembly 500 may be the upper portion 222 of the back panel 220,and may be selectively fastened to the lower portion 224 by thefastening means described herein, or by any means known to persons ofordinary skill in the art and capable of selectively attaching the stabassembly 500 to the lower portion 224.

It should be appreciated that the openings 226 defined for the stabassembly 500 in the MCU 200, or more particularly, the back panel 220,may be the same size regardless of the size of the MCU 200, e.g., a 12inch tall, 24 inch tall unit, etc. That is, while the dimensions, e.g.,height, width, depth, of the MCU 200 may differ, the openings 226 forany size MCUs 200 may be the same, which allows for the modularretractable stab assembly 500 to be mass produced. It should further beappreciated that the upper panel assembly 400 (FIG. 3A) or othersub-assembly disclosed herein may also be mass produced to fit any sizeMCU 200.

Referring now to FIGS. 6A-6C, an embodiment of a means for electricallydisconnecting the MCU 200 from one or more power buses 702 in shown. Themeans for electrically disconnecting the MCU 200, in an exemplaryembodiment, may be the retractable stab assembly 500. The stab assembly500 may include a stab housing 510 having one or more openings or slots512 adapted to at least partially receive therein or have attachedthereto one or more conductive contacts or stabs 510 (FIG. 6B). The stabhousing 510 may be made from a rigid polymer having electricalproperties, or any material known to persons of ordinary skill in theart and capable of having one or more stabs 520 fixedly attachingthereto. The stab housing 510 may be formed from a first housing section514 having one or more fastening apertures or recesses (not shown) forremovably attaching one or more stabs thereto, and a second housingsection 516 adapted to at least partially mate with the first housingsection 514. The second housing section 516 is the outermost portion ofthe stab housing 510, and may be frictionally fitted to the firsthousing section 514, or selectively attached thereto via a fasteningmeans. The second housing section 516 may further include a means foraccessing a power bus.

The means for accessing a power bus may be a access shoulder 518extending in a rearward direction from one side of the stab housing 510,e.g., the second housing section 516 in FIG. 6C, and be adapted tooperatively engage at least a portion of a shutter assembly 710 (FIG.7A) for moving one or more shutters of the shutter assembly 710 from afirst closed position (FIG. 7B) to a second open position (FIG. 7A) toallow for one or more stabs 520 to engage with a corresponding power bus702.

Referring now to FIGS. 5A-B, the stab assembly 500 may further include alead screw bracket assembly or lead screw bracket 550. In oneembodiment, the lead screw bracket 550 may be a single-piece of materialhaving one or more bends defining a first portion 552, second portion554, and third portion 556, selectively coupled to a mounting plate 560.In a further embodiment, the first 552, second 554, and third portion556, can be formed from separate pieces selectively attached to oneanother by, e.g., a fastening means, or be integrally formed asdescribed herein.

In the embodiment of FIG. 5A, the first 552, second 554, and thirdportions 556 are formed from a single piece of material bent in a mannerto define the first 552, second 554, and third portions 556. The firstportion 552 may have a length greater than the second 554 and thirdportions 556, and may be attached to the mounting plate 560, mountingbracket 570, or both. The second portion 554 may be disposed between thefirst 552 and third portion 556, and includes a lead screw opening 558adapted for at least partially receiving a lead screw 610 therebetween.The third portion 556 extends rearwardly from the second portion 554,and may be arranged substantially parallel to the first portion 552. Themounting plate 560 may be formed from a similar material to the leadscrew bracket 550, and may include one or more fastening apertures 562for selectively attaching the mounting plate 560 to the mounting bracket570. The mounting plate 560 may be attached to the mounting bracket 570by any of the fastening means described herein, or by other means knownto persons having ordinary skill in the art. In one embodiment, themounting plate 560 may have a thickness equal to or greater that thethickness of the mounting bracket 570, for providing support for thelead screw support bracket 550. However, it should be appreciated that athinner mounting plate 560 may be used depending on engineeringrequirements for the MCU 200, and chosen with sound judgment.

The stab assembly 500 may include one or more guide rail brackets 580for selectively attaching the stab assembly 500 to the back panel 220,and slideably engaging the mounting bracket 570. In an exemplaryembodiment, the guide rail bracket 580 may include one or more bentportions defining a guide rail bracket upper portion 582, and a guiderail bracket lower portion 584. As illustrated in FIG. 5A, the guiderail bracket upper portion 582 may include a means for slideablyengaging one or more stabs, i.e., one or more guide rails 590 extendingrearwardly therefrom for slideably engaging the mounting bracket 570,and lower portion 584 may be adapted to interface or be mounted to theback panel 220 for securing the guide rail bracket 580 to the back panel220. The guide rails 590 may be generally cylindrical, and adapted to beat least partially inserted between one or more openings (not shown) ofthe mounting bracket 570 for slideably engaging the mounting bracket 570along the guide rails 590. In the embodiment of FIG. 5A, two guide railbrackets 580 are shown, with each guide rail bracket 580 having a pairof guide rails 590 extending rearwardly from a side of the guide railbrackets 580. The guide rail brackets 580 may include one or moreopenings 585 for at least partially receiving a fastening meanstherebetween, and for selectively mounting the guide rails 590 to theguide rail brackets 580. In a further embodiment, the guide rails 590may be integral with the guide rail brackets 580, or be formed as asingle piece.

The guide rails 590 may be selectively attached to the back panel 220 byone or more guide rail holders 592 (FIG. 6B). The guide rail holders 592may have one or more bent portions defining at least a holder firstpotion 593 and a holder second portion 594. The holder first portion 593may include an opening for at least partially receiving the guide rail590 therebetween. The guide rail 590 may be selectively secured to theholder 592 by weld or any other means known to persons of ordinary skillin the art, and capable of securing the guide rail 590 to the holder592. The guide rail holder second portion 594 may be adapted tointerface with the upper portion 222 the back panel 220 to providefurther support for selectively securing the stab assembly 500 to theback panel 220. In the embodiment of FIG. 6B, each guide rail 590 isshown having at least one guide rail holder 592 attached thereto forsecuring the same to the upper portion 222. It should be appreciated,that the guide rail holder 592 may be utilized for securing the guiderail 590, and not for restricting the slideable engagement between theguide rails 590 and the mounting bracket 570.

With continue reference to FIG. 5A, an exemplary embodiment of a leadscrew assembly 600 is shown. The lead screw assembly 600 may comprise alead screw 610 having a body portion 615 and a head portion, and one ormore nuts or stoppers (630, 632) for limiting axial movement of theretractable stab assembly 500. The body portion 615 may be any shape,and have at least a portion thereof threaded for interfacing with athreaded portion of the stoppers (630, 632). In the embodiment of FIG.5A, the body portion 615 is generally cylindrical, however, the bodyportion 615 may be any polygon shape known in the art. The head 620 mayalso be generally cylindrical or any polygon shape, and includes one ormore voids or recesses 622 adapted to interface with a lead screw tool(not shown) or an actuating device (not shown). As shown in FIG. 5A, thevoid 622 defines a first head portion 624 and a second head portion 626.The void 622 may be non-uniform or uniform around the perimeter of thehead 620, and may be adapted or sized such that at least a portionthereof is adapted to at least partially receives a potion of a firstlead screw head support bracket 440 and a second lead screw head supportbracket 442 (FIG. 3B) therebetween, for providing support for the leadscrew assembly 600.

The first 440 and second 442 lead screw head brackets may be part of thelead screw assembly 600, or as shown in the embodiment of FIG. 3B, apart of the upper panel assembly 400. The first 440 and second 442 leadscrew head support brackets may include one or openings for operablyconnecting to one or more adjacent panels of the MCU 200, or as shown inFIG. 3D, the upper assembly panel 400. The first lead screw head supportbracket 440 may further include one or more bends defining a first upperportion 444 and second lower portion 445. The first upper portion 444may be adapted to selectively attach the same to a structure in theupper panel assembly 400, e.g., via a fastening means. The structure maybe moveable or fixed. The second lower portion 445 may be adapted toselectively attach the same to one or more openings in the second leadscrew head support bracket 442. In one embodiment, the first 440 andsecond 442 lead screw brackets may include at least a portion thereofhaving a polygonal or arcuate profile adapted to interface with the void622, such that vertical and or horizontal movement of the head 620 maybe limited. Similar to the first lead screw head support bracket 440,the second lead screw head support bracket 442 may include one or morebends defining at least a first bend portion 446 and a second bendportion 447. In the embodiment of FIG. 3C, the first bend portion 446may include one or more openings for receiving a fastening means atleast partially therebetween for selectively attaching the second leadscrew head support bracket 442 to the first lead screw head supportbracket 440.

The second bend portion 447 may further include one or more openingsadapted for receiving a fastening means therebetween, or as shown inFIG. 3D, at least a portion of an indicator assembly 470 therebetween.Status indicators of the indicator assembly 470 may be viewed via theindicator opening 232. The indicator assembly 470 may be formed from asingle-piece of material, or be formed from a plurality of framesselectively attached together by any of the fastening means describedherein. The indicator assembly 470 may include a first indicator portion472 having status indications (e.g., live, engaged, disengaged, deadetc.) for providing the status of the MCU 200, and a second indicatorportion 474 adapted to operationally shift from a first position to asecond position which may correspond with the shifting of at least aportion of the upper panel assembly 400, e.g., the access bracket 414.

The stoppers (630, 632) may be made from a metallic material similar tothat of the lead screw body, or any material known to persons ofordinary skill in the art and adaptable to restrict movement of the leadscrew 610 and/or stab assembly 500. The stoppers (630, 632) may alsoinclude a threaded portion corresponding with the threaded portion ofthe lead screw 610. The first stopper 630 may have a similarconfiguration to that of the second stopper 632.

In the embodiment of FIGS. 5A and 5B, at least one of the stoppers (630,632), may be operably adapted to axially shift along the body portion615 of the lead screw 610 when the stab assembly 500 shifts from a firstengaged position (see FIG. 5A) to a second disengaged position (see FIG.5B). The first stopper 630 and the second 632 may abut one another whenthe stab assembly 500 is in the engaged position (FIG. 5A), and bespaced apart when the stab assembly 500 is in the disengaged position(FIG. 5B). The first stopper 630 may be selectively mounted to thesecond portion 554 of the lead screw support bracket 550, e.g., viafastening means or welding, such that movement of the stab assembly 500corresponds with the movement of the first stopper 630 along the axis ofthe lead screw. The second stopper may include a restrictor plate 634mounted at one end of the second stopper 632 to restrict axial movementof the second stopper 632 along the lead screw 610. For example, therestrictor plate 634 in FIG. 5B may limit the lead screw 610 fromextending beyond the restrictor plate 634 by not including an opening orhaving an opening with a smaller size (e.g., smaller diameter) that thediameter of the body portion 615.

Referring now to FIGS. 7A-B, front perspective views of a shutterassembly 710 are provided. The shutter assembly 710 may include ashutter plate 712 operably coupled to an access bracket assembly 720.The shutter plate 712 may include one or more fastening apertures 714adapted for slideably mounting the shutter assembly 710 to the power bushousing 700. In the embodiment shown in FIGS. 7A-B, the shutter plate712 includes at least four (4) fastening apertures 714 slideablymounting the shutter plate 712 to the power bus housing 700. The shutterplate 712 may further include one or more shields 716 for blockingaccess to one or more corresponding power buses 702 within the power bushousing 700 in a first position, e.g., a closed position. The shutterplate 712 further include one or more power bus apertures 718 that maybe offset from the fastening apertures 714 for providing access to thepower buses 702 in a second position, e.g., an open position. The powerbus apertures 718 may be generally spaced an equidistance apart, and maybe shaped/adapted to at least partially receive a stab 520 therebetweenfor interfacing with the power bus 702.

With continued reference to FIGS. 7A-B, the access bracket assembly 720may further include an access bracket panel 722 having one or moreaccess bracket frame fastening apertures (not shown) for selectivelymounting the access bracket panel 722 to the power bus housing 700, or astructure proximate to the power bus housing 700. The access bracketpanel 722 may include one or more grooves (not shown) adapted toslideably engage a means for moving the shutter plate 712 from the firstposition to the second position. In one embodiment, the means for movingthe shutter plate 712 may be a biasing member (not shown), for example,a spring loaded mechanism configured for shifting the shutter plate 712from the first position to the second position. The access bracketassembly 720 may further include an extender piece 724 adapted tointerface with at least a portion of the stab assembly 500, e.g., theaccess arm or shoulder 518, for moving the shutter plate from a closedposition to an open position when extending the retractable stabassembly 500 towards to the power bus housing 700 for engaging one ormore stabs 520 with one or more corresponding power buses 702. Inoperation, the interfacing between the access shoulder 518 and theextender piece 724 may cause a spring of the spring mechanism tocompress as the shutter plate 712 moves from the closed position to theopen position.

With reference now to FIG. 8, an embodiment of a method 1000 forservicing a motor control unit is provided. It should be appreciatedthat following steps are not required to be performed in any particularorder, and are hereby provided for exemplary purposes. For example,steps for disengaging one or more stabs may not be necessary where thestabs were previously disengaged, and/or where a motor control unit haspreviously been removed from its compartment.

In step 1010, moving the switch 310 from a first on position to a secondoff position. In this step, by moving the switch to the off position,power to one or more electrical components within the motor control unitmay be interrupted. In an exemplary embodiment, moving the switch 310 tothe second position may shift at least a portion of the upper panelassembly, e.g., the first support bracket 402, in a downwards directionthereby providing access to the lead screw 610 via the access bracket414. In step 1020, disengaging the stabs 520 from the power bus 702. Inembodiments where the motor control unit includes fixed stabs, pullingout the motor control unit via a handle, for example, may disengage thestabs. In embodiments where the MCU 200 includes the retractable stabassembly 500, the step of disengaging the stabs may include the step of:inserting at least a portion of a lead screw tool into the opening 416,and shifting (e.g., rotating) the lead screw 610 from a first positionto a second position, thereby retracting the stab assembly 500 in adirection towards the front panel 210, and disengaging the stabs 520from the power bus 702.

In step 1030, removing the MCU 200 from the MCC section 110. Aspreviously described, in embodiments of the motor control units havingfixed stabs, removing the motor control unit may inherently disengagethe stabs. In step 1040, disassembling the stab assembly. In step 1050,installing the retractable stab assembly 500 in the MCU 200. In step1060, at least partially inserting the MCU 200 having the retractablestab assembly 500 into the compartment of the MCC section 110, andengaging one or more stabs 520 with the power bus 702. In this step,engaging the one or more stabs may be accomplished by extending the stabassembly 500 rearwardly by, for example, rotating the lead screw 610 inan engaging direction.

With continued reference to the figures and now FIG. 9, an exemplaryembodiment of a remote-controlled system 10 for operating an embodimentof the MCU 200 is provided. The system 10 may include a remote-device orpendant 20 operatively connected to one or more embodiments of amotorized MCU 200, i.e., a motorized control unit 800. The connection 15between the pendant 20 and the motorized control unit 800 may be wired,via one or more cables, or wireless, via one or more wirelesstransceiver of the motorized control unit 800 and the pendant 20.

In one embodiment, the pendant 20 may include a memory (not shown) forstoring executable instructions, e.g., instructions to activate anddeactivate the motorized control unit 800, and a processing circuitoperable to execute the stored instructions. The pendant 20 may furtherinclude one or more buttons or control knobs 24 for operating themotorized control unit 800. In operation, shifting the button or knob 24may cause the processing circuit to execute instructions correspondingto the shift, e.g., a shift in the first direction may activate themotorized control unit 800, while a shift in a second direction maydeactivate the motorized control unit 800. It should be appreciated,that execution of the instructions may generate control signals whichare transmitted to the motorized control unit 800 for operating thesame. The control signals may be transmitted to the motorized controlunit 800 via one or more cables in a wired connection or via thewireless transceiver in a wireless network environment. The pendant mayfurther include one or more indicators 22 for identifying a status ofthe motorized control unit, i.e., whether the motorized control unit 800is active (stabs engaged) or inactive (stabs disengaged). The pendant 20may also include a display 26 for displaying the status of the motorizedcontrol unit 800.

With reference to FIG. 10, an embodiment of the motorized control unit800 is provided. The motorized control unit 800 may be similar to theMCU 200 in that in may include a housing 802 adapted to at leastpartially enclose one or more electrical components therein, e.g., theswitch assembly 300, upper panel assembly 400, retractable stab assembly500, and lead screw assembly 600. In the embodiment of FIG. 10, inaddition to the sub assemblies, the motorized control unit 800 comprisea motor assembly 900 operatively connected to a front panel of thehousing 802.

The motor assembly 900 may include a drive motor 910 operativelyconnected to a drive shaft 920 and power adapter 930. The power adapter930 may include one or more openings adapted to receive one or morecables for operating the motor assembly 900. The cables may be cablesoperatively connected to the pendant 20 for facilitating thetransmission of the control signals to drive the drive motor 910.Additional cables may also be operatively connected to the power module930 for connecting to a power source for powering the electricalcomponents within a housing 902 of the motor assembly 900, e.g., thedrive motor 910. In yet a further embodiment, the motor assembly 900 maybe powered by a battery or other means for powering a drive motor 910known to persons of ordinary skill in the art. In yet a furtherembodiment, the power adapter 930 may include a wireless transceiver forfacilitating the wireless communication between the pendant 20 and themotor assembly 900.

With continued reference to the figures and now FIGS. 11-14, the drivemotor 910 may be operatively connected to the pendant 20 for receivingcontrol signals for providing a motive force to rotate the drive shaft920 in multiple directions to operate the motorized control unit 800. Inan exemplary embodiment, the drive shaft 920 may extend rearwardly fromthe housing 902 such that the drive shaft 920 interfaces with the leadscrew 610. In yet a further embodiment, the housing 902 may include backplate 904 with a drive shaft opening 906 adapted for the drive shaft 920to extend at least partially therethrough for interface with the leadscrew 610 when the motor assembly 900 is attached to the motorizedcontrol unit 800. It should be appreciated, in a further embodiment,that one or more seals or adapters may be provided at the drive shaftopening 906 for interfacing with or supporting the drive shaft 920extending rearwardly therefrom. The housing 902 may further include oneor more mounting brackets 908 disposed on opposite sides of the housing902 for selectively attaching the motor assembly 900 to the front of thehousing 802.

In one embodiment, the mounting brackets 908 may include a recess havingan arcuate profile for interfacing with one or more mounting arm (notshown) on the front of the housing 802 for attaching the motor assembly.It should be appreciated that in addition to or in lieu of the recess,the mounting brackets 908 may further include an aperture or hole forreceiving fasteners for securing the motor assembly 900 to the housing802, via a corresponding aperture adapted for receiving the fasteners.In yet a further embodiment, the mounting brackets 908 may be attachedto or integrally formed with the back plate 904 for attaching the motorassembly 900 to the motorized control unit 800. A handle 940 may also beprovided at an upper portion of the housing 902 for facilitating theattaching and removal of the motor assembly 900 from the housing 802.

In yet a further embodiment, the operability of the motor assembly 900may correspond with the functionality of the switch assembly 300, andmore particularly, the switch 310, and e.g., whether or not it is in anon or off position. For example, in one exemplary embodiment, anoperator may not be able to switch the switch assembly 300 on unless theretractable stab assembly is fully retracted or extended. Additionally,the switch 310 may also not be moveable to the on position if the leadscrew 610 is being rotated, e.g., by the drive shaft or any externaltool. In yet a further exemplary embodiment, no access to the lead screwaccess opening 218 may be provided if the switch is in the on position,thus the motor assembly 900 may not be able to attach to the front ofthe housing 802 because the drive shaft 920 may not have access to thelead screw 610 with a closed/blocked lead screw access opening 218.

With continued reference to the figures, the drive shaft 920 may extendrearwardly beyond the back of the housing 902 or back plate 904 to allowfor the drive shaft 920 to be at least partially inserted into the leadscrew access opening 218. Once the drive shaft is inserted into the leadscrew access opening 218, the drive shaft may interface or engage thelead screw 610 such that rotation of the drive shaft 920, via the drivemotor 910, causes the lead screw 610 to rotate, which extends andretracts the retractable stab assembly 500 to engage and disengage thestabs. In yet a further embodiment, the drive shaft 920 may be used inlieu of the lead screw 610 in that the drive shaft 920 may extend atleast partially through the lead screw opening 558 for attaching theextended drive shaft 920 to the stoppers 630, 632, for limiting axialmovement of the retractable stab assembly 500 in operation.

With reference now to FIG. 15, a flow chart for a method 1500 ofdisengaging stabs of an exemplary embodiment of the motorized controlunit is provided. It should be appreciated that following steps are notrequired to be performed in any particular order, and are herebyprovided for exemplary purposes.

In step 1510, the drive motor 910 is initiated, via the pendant 20, toengage the stabs of the retractable stab assembly 500. It should beappreciated that if the motor assembly 900 has not been previouslyattached to the motorized control unit 800, or more particularly thehousing 802, an operator may attach the motor assembly 900, e.g., usingthe handle 940, to the housing 802 prior to initiating the drive motor910. It should further be appreciated, as described herein, that beforeattaching the motor assembly 900, the motorized control unit 800 switch310 should be in the off position, which allows for the drive shaft 920to extend through the lead screw access opening 218 to engage the leadscrew 610. Upon attaching the motor assembly 900, the operator mayinitiate the drive motor 910 by selecting a button or shifting the knob24 in a first direction to extend the retractable stab assembly 500rearwardly towards the power bus 702 to engage the stabs with the powerbus 702. Shifting the knob 24 may cause the processing circuit of thependant 20 to execute instructions for rotating the drive shaft 920 andto generate control signals corresponding to the instructions. Thecontrol signals may then be transmitted to the motor assembly 900, ormore particularly the drive motor 910, from the pendant 20, whichrotates the drive shaft 920 in a first direction to engage the stabswith the power bus 702. In this embodiment, rotation of the drive shaft920 causes the lead screw 610 to rotate, which results in theretractable stab assembly 500 shifting along the guide rails 590 in adirection to engage the stabs.

Once the stabs are engaged, in step 1520, a confirmation of thesuccessful engagement may be transmitted from the motorized control unit800 to the pendant 20 and displayed, e.g., on the display 26. Thesuccessful engagement/connection confirmation from the motor assembly900 may be based on or results from, e.g., the lead screw 610 no longerbeing rotated in the engaging direction, i.e., the lead screw 610 hasstop rotating in a direction extending the retractable stab assembly 500towards the power bus 702. It should also be appreciated that the leadscrew 610 no longer rotating in the disengaging direction may beindicative of the retractable stab assembly being in the fully retractedposition and the stabs being disengaged from the power bus 702. Itshould further be appreciated that other circuitry may be provided andactivated upon the retractable stab assembly 500 being in a fullyextended and engaged position, or fully retracted and disengagedposition. The circuitry may then transmit this information, i.e., theassembly is fully extended, as an engagement signal to the connectedpendant 20 for engagement confirmations, and as a disengagement signalfor disengagement confirmations.

In step 1530, the operator may then remove the motor assembly 900, e.g.,via the handle 940, from the motorized control unit 800, or moreparticularly, the housing 802, and upon receiving the engagement signalfrom the motorized control unit 800 or motor assembly 900. In a furtherembodiment, to disengage the motorized control unit 800, in step 1540,the operator may switch the switch 310 to the off position, whichprovides access to the lead screw 610, via the lead screw access opening218 being available with the switch 310 in the off position. Theoperator may then attach the motor assembly 900 to the housing 802 suchthat the drive shaft 920 extends through the lead screw access opening218 and interfaces with the lead screw 610. The operator may then beginretracting the retractable stab assembly 500 to disengage the stabs fromthe power bus 702. To begin retracting the stab assembly 500, theoperator may select a button or shift the knob 24 which may generate andtransmit a disengage control signal from the pendant 20 to the motorassembly 900 which causes the drive motor 910 to rotate the lead screw610, e.g., by way of the drive shaft 920, in a direction opposite theengagement direction or a further direction, which retracts theretractable stab assembly 500 away from the power bus 702 along an axisof the guiderails.

It should be appreciated that one button or knob 24 may be used on thependant 20 for extending or retracting the retractable stab assembly500. It should further be appreciated that a further signal may betransmitted from the motorized control unit 800 or motor assembly 900 tothe pendant 20 identifying that the motorized control unit 800 isdisengaged, i.e., the disconnection between the stabs and the power bus702 is complete. Once the stabs have been disengaged from the power bus700, the motor assembly 900 may be removed from the motorized controlunit 800, via the handle 940.

While specific embodiments have been described in detail, those withordinary skill in the art will appreciate that various modifications andalternative to those details could be developed in light of the overallteachings of the disclosure. For example, elements described inassociation with different embodiments may be combined. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andshould not be construed as limiting the scope of the claims ordisclosure, which are to be given the full breadth of the appendedclaims, and any and all equivalents thereof. It should be noted that theterms “comprising”, “including”, and “having”, are open-ended and doesnot exclude other elements or steps; and the use of articles “a” or “an”does not exclude a plurality.

We claim:
 1. A system for operating a control unit in a motor controlcenter comprising: a pendant; a motorized control unit operativelyconnected to the pendant and configured to receiving control signalsfrom the pendant, the motorized motor control unit comprising: a housingadapted to at least partially enclose one or more electrical componentstherein; a retractable stab assembly enclosed within the housing andincluding one or more stabs for engaging a power bus in the motorcontrol center; a motor assembly selectively attached to a front of thehousing and operatively connected to the retractable stab assembly forextending and retracting the retractable stab assembly in response tothe control signals for engaging and disengaging the one or more stabs;and a lead screw assembly disposed between a drive shaft and theretractable stab assembly, the lead screw assembly including: a leadscrew adapted to rotate in opposed direction to engage and disengage theone or more stabs; and first and second stoppers adaptable to restrictmovement of the lead screw for limiting axial movement of theretractable stab assembly, wherein the first and second stoppers areoperably adapted to axially shift along a body portion of the lead screwwhen the retractable stab assembly shifts from a first engaged positionto a second disengaged position such that the first stopper and thesecond stopper abut one another when the retractable stab assembly is inthe first engaged position and be spaced apart when the retractable stabassembly is in the second disengaged position.
 2. The system of claim 1,wherein the motor assembly further comprises: a drive motor operativelycoupled to the drive shaft, and wherein the drive motor receives thecontrol signal from the pendant and rotates the drive shaft in responseto the control signals for extending and retracting the retractable stabassembly.
 3. The system of claim 1, wherein the drive shaft interfaceswith the lead screw for rotating the lead screw in response to thecontrol signals.
 4. The system of claim 3, wherein the motor assemblycomprises: a back plate having a shaft opening adapted to at leastpartially receiving the drive shaft therethrough, and wherein the shaftopening corresponds with a lead screw opening in the front of themotorized control unit for interfacing the drive shaft to the leadscrew.
 5. The system of claim 4, wherein the back plate includesmounting brackets for selectively attaching the motor assembly to thefront of the motor control unit.
 6. The system of claim 1, wherein themotorized control unit further comprises: a handle selectively attachedto an upper portion of the housing.
 7. The system of claim 1, whereinthe motor assembly further comprises: mounting brackets disposed onopposite sides of the motor assembly, each mounting bracket comprising arecess or aperture for selectively attaching the motor assembly to acorresponding adapter on the front of the motorized control unit.
 8. Thesystem of claim 1, wherein the motor assembly further comprises: a poweradapter having one or more cables connecting the pendant to the motorassembly.
 9. A motorized control unit for a motor control centercomprising: a housing for at least partially enclosing one or moreelectrical components therein; a retractable stab assembly mountedwithin the housing and including: a stab housing having one or morestabs extending rearwardly therefrom, the stab housing adapted toslideably engage guide rails within the motorized control unit forextending and retracting the retractable stab assembly; and a lead screwassembly operatively connected to the stab housing and including a leadscrew rotatable to extend and retract the retractable stab assemblyalong the guiderails; and a motor assembly selectively attached to afront of the housing, the motor assembly including: a drive motoroperatively coupled to a drive shaft, wherein the drive shaft extends ina rearward direction to engage the lead screw within the housing; andwherein the drive motor is operable to rotate the lead screw, via thedrive shaft, wherein the lead screw assembly including: first and secondstoppers adaptable to restrict movement of the lead screw for limitingaxial movement of the retractable stab assembly, wherein the first andsecond stoppers are operably adapted to axially shift along a bodyportion of the lead screw when the retractable stab assembly shifts froma first engaged position to a second disengaged position such that thefirst stopper and the second stopper abut one another when theretractable stab assembly is in the first engaged position and be spacedapart when the retractable stab assembly is in the second disengagedposition.
 10. The motor control unit of claim 9, wherein the drive motorrotates the drive shaft in response to control signals from a pendantoperatively connected thereto.
 11. The motor control unit of claim 9,wherein the motor assembly further comprises: a handle selectivelyattached to an upper portion of the motor assembly.
 12. The motorcontrol unit of claim 9, wherein the motor assembly further comprises:mounting brackets on opposed sides of the motor assembly for attachingthe motor assembly to the front of the motor control unit.
 13. The motorcontrol unit of claim 12, wherein each mounting bracket comprises arecess for attaching the motor assembly to the front of the motorcontrol unit.
 14. A motor control center comprising: a control centersection including one or more compartments having a motorized controlunit according to claim 9 at least partially secured therein; and apendant operatively attached to the motor assembly and configured totransmit control signals to the drive motor for extending and retractingthe retractable stab assembly.
 15. The motor control center of claim 14further comprising: a power bus housing comprising a power bus; andwherein the one or more stabs are adapted to engage the power bus, viarotation of the drive shaft in a first direction, in response to a firstcontrol signal.
 16. The motor control center of claim 15, wherein theone or more stabs are adapted to disengage from the power bus, viarotation of the drive shaft in a second direction opposite the firstdirection, in response to a second control signal.
 17. A method foroperating a motorized control unit in a motor control center accordingto claim 14, comprising the step of: initiating the drive motor, viacontrol signals from the pendant, which causes the drive shaft to rotatein a first direction resulting in the retractable stab assemblyextending towards a power bus for engaging the one or more stabs withthe power bus.
 18. The method of claim 17, wherein the step ofinitiating the drive motor comprises the step of: shifting a knob of thependant in a first direction to generate and transmit control signalsfrom the pendant to the motor assembly for engaging the one or morestabs with the power bus.
 19. The method of claim 17 further comprisingthe step of: removing the motor assembly from the motorized control unitupon receiving confirmation from the motorized control unit that theretractable stab assembly is fully extended and the one or more stabsare engaged.
 20. The method of claim 19 further comprising the step of:attaching the motor assembly to the motorized control unit; and rotatingthe drive shaft in a second opposite or further direction from the firstdirection which causes the retractable stab assembly to retract awayfrom the power bus to disengage the one or more stabs.
 21. The method ofclaim 20, wherein the step of rotating the drive shaft in the secondopposite or further direction is caused by shifting a knob of thependant in a second direction to generate and transmit control signalsfor initiating the drive motor to disengage the one or more stabs fromthe power bus.